The Tolkien character known as Gollum was originally named Sméagol.
Sméagol was a river-hobbit-like being who found the One Ring after his relative Déagol discovered it in the Anduin. Sméagol killed Déagol to take the ring, and the act began his long moral and physical decline. The ring’s influence and his isolation eventually transformed him into the creature called Gollum, a name derived from the swallowing or choking sound he made.
By the time Bilbo encounters him beneath the Misty Mountains in The Hobbit, Gollum has lived in darkness for centuries. In The Lord of the Rings, he becomes crucial to the ring’s destruction because his obsession leads him to Mount Doom, where the Ring is finally destroyed.
Déagol is often mistaken for Gollum’s earlier name, but Déagol is the relative who finds the Ring first. Sméagol is the correct original name.